The present invention relates to connector blocks used within connectors of implantable pacemakers. More particularly, the present invention relates to a connector block and method of attachment thereto which secures electrical contact with the proximal ring electrode of a bipolar pacing lead in a manner that prevents the proximal ring electrode from being damaged or deformed.
It is common practice in the pacemaker art to employ pacemaker leads that include two separate connectors. Such two-conductor leads are referred to in the art as "bipolar" leads. (Bipolar leads are usually realized with helically-wound coaxial conductors, one inside the other, with a layer of insulating material therebetween. However, the invention described herein is not intended to be limited to or by such coaxial conductor configurations.)
At the proximal end (that is, the end that is to be connected to the pacemaker) of such bipolar leads it is common to employ a tip electrode and a ring electrode, each electrode being connected to one of the conductors within the lead. The tip electrode is typically made from a rigid tube having thick or heavy walls. (A channel or hole passing through the center of this thick-wall tip electrode provides a convenient means for introducing a stylet into the lead.) Due to the thickness of the walls of the proximal tip electrode, a firm electrical connection can be made thereto, as well as a firm physical connection (to prevent the electrode from inadvertently becoming disconnected from the pacemaker) by transversely driving a setscrew thereagainst. The setscrew is anchored in a suitable connector block that forms part of the "connector" of the pacemaker. (The "connector" of a pacemaker is that portion designed to receive the pacemaker lead). The connector block has a recess or channel therein into which the tip electrode is inserted. (The recess of the connector block may be thought of as the female component of a conventional connector; and the tip electrode may be thought of as the male component.) The setscrew assures firm electrical contact between the male and female components and physically locks or holds the male/female components together. (The connector block, in turn, is electrically connected to the appropriate pacemaker circuits.) A further description of this type of connection technique, including some of the problems associated therewith, as used with respect to a proximal tip electrode, can be found in U.S. Pat. No. 3,908,668.
In contrast to the rigid, strong thick-wall proximal tip electrode, the proximal ring electrode of a bipolar lead is rather delicate and easily deformed. As its name implies, the ring electrode is a ring. In order to allow the proximal tip conductor and insulation to pass therethrough, the ring electrode by necessity has thin walls. Hence, the proximal ring electrode may be easily deformed or otherwise damaged in setscrew-type connector blocks.
Despite the rather delicate nature of a proximal ring electrode, setscrew-type connector blocks are nonetheless commonly used in the art in order to make electrical contact therewith. In such arrangements, a second connector block (separate or insulated from the first connector block with which the tip electrode makes contact) has a recess or opening therethrough into which the ring electrode is inserted. A second setscrew, threadably engaged with the second connector block, is then screwed against the ring electrode in order to make firm electrical contact therewith. However, great care must be exercised when the set screw is adjusted in order to prevent deformation of the ring electrode. Such deformation could not only render the lead unusable in the future (should the pacemaker have to be subsequently replaced), but it could also render the lead inoperable. For example, the ring could be deformed to the point that the ring does not easily fit within the opening of its connector block, or is tightly wedged therein. In either event, insertion and removal forces could easily exceed those forces for which the lead was designed. In severe cases of ring deformation, the inner conductor could even be shorted to the outer conductor. Inasmuch as it is highly desirable to be able to leave a lead in place within a patient once implanted (so as to reduce any trauma or shock that might accompany insertions and removals of pacing leads into and out of the heart), and therefore to be able to reuse the implanted lead over and over again with as many different pacemakers as may be required, it is important that the integrity of the proximal electrodes be maintained. Hence, there is a need in the art for a pacemaker connector block that can make firm and reliable electrical contact with a proximal ring electrode without subjecting the ring electrode to the risk of deformation or other damage. The present invention is directed to this need.